Subsequent Chemical Activation Research Articles

One‐pot emulsion templating for simultaneous hydrothermal carbonization and hydrogel synthesis: porous structures, nitrogen contents and activation

AbstractPorous carbons are of interest for a wide range of advanced‐technology ‘green’ energy applications including fuel cells, hydrogen storage, supercapacitors and batteries. Functional groups, heteroatoms and a more accessible hierarchical porous structure would be advantageous for many of these applications. This paper describes the generation of carbonaceous monoliths with hierarchically porous structures and nitrogen functionalities by using a one‐pot, simultaneous combination of hydrogel synthesis and hydrothermal carbonization (HTC) that involves templating within high internal phase emulsions (HIPEs). A carbon monolith with a density of 0.058 g cm−3, a highly interconnected, bimodal porous structure and an apparent specific surface area (SBET) of 101 m2 g−1 was produced by carbonizing a HTC monolith based on 2‐hydroxyethyl methacrylate (HEMA) at 450 °C. SBET of 1540 m2 g−1 was produced through subsequent chemical activation with ZnCl2 at 700 °C, but the overall residual mass (Rm) was only 9 wt%. Direct chemical activation of the HTC monolith, on the other hand, generated SBET of 1250 m2 g−1 and an overall Rm of 28 wt%, corresponding to a higher apparent surface area per mass of HTC monolith. Carbon monoliths with N/C ratios of 0.09 and 0.07 were achieved using nitrogen‐rich monomers (acrylamide and vinylimidazole, respectively) as compared to the HEMA‐based carbon monolith with an N/C ratio of 0.03. This work demonstrates that the hierarchically porous structures and the chemical structures of these highly porous monoliths can be fine‐tuned by modifying the HIPE composition and/or the processing conditions. © 2021 Society of Industrial Chemistry.

Metal oxide-doped activated carbons from bakery waste and coffee grounds for application in supercapacitors

The functionalization of sustainable carbon materials and their application in energy storage systems attract more and more relevancy. Bakery waste and spent coffee grounds were chosen as abundant organic residues and found to be suitable starting materials for hydrothermal carbonization and a subsequent chemical activation obtaining carbon contents of > 88%. In situ doping of the hydrochars during carbonization has proven to be a successful method for insertion of Fe2O3-, Fe3O4- and MnO2-Nanoparticles into the carbon matrix, supported by XRD analysis and SEM images. Chemical activation with K2CO3 led to iron contents up to 18% of iron and around 8% of manganese, respectively, in the corresponding activated carbon. Electrochemical characterization revealed overall higher specific capacitance for activated carbons derived from spent coffee grounds, with a highest of 87F*g−1. In contrast, the highest specific capacitance measured for activated carbons originated from bakery waste was 40,3F*g−1.

Super-activated CNB for CO2 capture: The development of the nitrogen containing porous carbon by chlorination and post KOH-activation

Minimization of carbon dioxide (CO2) emissions into the atmosphere is a prerequisite to solving climate change. Tremendous research has been conducted to capture the CO2 from pre- and post-combustion using nanoporous materials. Nitrogen-doped porous carbon is one of the most promising CO2 adsorbents. Achieving high nitrogen content and high micropore volume is essential to CO2 adsorption properties. In this study, super activated nitrogen and boron co-doped porous carbons (K-CNBs) are successfully synthesized by the chlorination and the subsequent KOH chemical activation. Nitrogen and boron co-doped porous carbons (CNBs) are synthesized by the chlorination of titanium carbonitride and boride mixture. CNBs good thermal and oxidation stability that induces an increase in the nitrogen content as well as an increase in the micropore volume even after the activation. K-CNBs, having both high micropore volume and abundant pyridonic-N functional group, show superior CO2 uptake at ambient temperature at atmospheric pressure with excellent CO2/N2 selectivity. K-CNBs are the best CO2 capturer among the nitrogen-containing carbon materials, reaching the threshold of CO2 uptakes performance.

Preparation of a quinoa straw-derived porous carbon material and a Fe3O4-contained composite material for removal of rhodamine B from water

In this work, quinoa straw (QS) is considered as a sustainable biomass resource to produce adsorbent materials for wastewater treatment. Two materials, a porous carbon material derived from QS (PCQS) and a Fe3O4-containing composite material based on the PCPS (Fe3O4@PCQS), were prepared. PCQS was prepared via carbonization and subsequent chemical activation of the QS using NaOH. Thereafter, PCQS was characterized by SEM, TEM, XRD, IR, XPS, and N2 adsorption-desorption analysis. As a carbon material with heterogeneous pores, PCQS has a BET specific surface area of 3435.21 m2 g−1, which is about 175 times higher than that of the precursor QS (19.60 m2 g−1). The PCQS had an adsorption capacity of 1778.1 mg g−1 toward rhodamine B (RhB), and the adsorption followed pseudo-second-order kinetics and the Freundlich isotherm model. The PCQS was further modified by synthesizing Fe3O4 magnetic nanoparticles on the surface of PCQS to give Fe3O4@PCQS. The adsorption capacity of Fe3O4@PCQS toward RhB reached 1156.2 mg g−1, and it could be rapidly separated from water by applying an external magnetic field. The PCQS and Fe3O4@PCQS exhibited acceptable reusability which was evaluated through ten successive adsorption/desorption cycles. In summary, the adsorption capacities of PCQS and Fe3O4@PCQS toward RhB are comparable with most current adsorbents, including the graphene-based materials, which shows that QS is a promising biomass feedstock to prepare carbon-based materials and composites.

Engineering Kinetics-Favorable Carbon Sheets with an Intrinsic Network for a Superior Supercapacitor Containing a Dual Cross-linked Hydrogel Electrolyte.

Despite the physicochemical advantages of two-dimensional (2D) carbons for supercapacitors, the inappropriate texture within 2D carbon materials suppresses the charge storage capability. Reported here are heteroatom-rich carbon sheets with the overall network engineered by molecular structure modulation and subsequent chemical activation of a three-dimensional (3D) cross-linked polymer. The 3D-to-2D reconstruction mechanism is unveiled. The architecture with a large active surface, fully interpenetrating and conductive network, and rich surface heteroatoms relieves well the ionic diffusion restriction within thick sheets and reduces the overall resistance, exhibiting fast transport kinetics and excellent stability. Indeed, high gravimetric capacitance (281.1 F g-1 at 0.5 A g-1), ultrahigh retention rate (92.5% at 100 A g-1), and impressive cyclability (89.7% retention after 20 000 cycles) are achieved by this material. It also possesses a high areal capacitance of 3.56 F cm-2 at 0.5 A g-1 under a high loading of 25 mg cm-2. When coupled with the developed dual cross-linked hydrogel electrolyte (Al-alginate/poly(acrylamide)/sodium sulfate), a quasi-solid-state supercapacitor delivers an energy density of 28.3 Wh kg-1 at 250.1 W kg-1, which is significantly higher than those of some reported aqueous carbon-based symmetric devices. Moreover, the device displays excellent durability over 10 000 charge/discharge cycles. The proposed cross-linked polymer strategy provides an efficient platform for constructing dynamics-favorable carbon architectures and attractive hydrogel electrolytes toward improved energy supply devices.

Encapsulation of Se into Hierarchically Porous Carbon Microspheres with Optimized Pore Structure for Advanced Na-Se and K-Se Batteries.

Sodium-selenium (Na-Se) and potassium-selenium (K-Se) batteries have emerged as promising energy storage systems with high energy density and low cost. However, major issues such as huge Se volume changes, polyselenide shuttling, and low Se loading need to be overcome. Although many strategies have been developed to resolve these issues, the relationship between the carbon host pore structure and electrochemical performance of Se has not been studied extensively. Here, the effect of the carbon host pore structure on the electrochemical performance of Na-Se and K-Se batteries is investigated. N, S-co-doped hierarchically porous carbon microspheres with different pore structures that can incorporate a large amount of amorphous Se (∼60 wt %) are synthesized by spray pyrolysis and subsequent chemical activation at different temperatures. By optimizing the amount of micropore volume and micropore-to-mesopore ratio, high reversible capacity and cycling stability are achieved for the Se cathode. The optimized cathode delivers a reversible capacity of 445 mA h g-1 after 400 cycles at 0.5C for Na-Se batteries and 436 mA h g-1 after 120 cycles at 0.2C for K-Se batteries. This study marks the importance of developing conductive carbon matrices with delicately designed pore structures for advanced alkali metal-chalcogen battery systems.

Preparation of Highly Porous Graphitic Activated Carbon as Electrode Materials for Supercapacitors by Hydrothermal Pretreatment-Assisted Chemical Activation.

The obstruction of traditional chemical activation lies in the addition of excessive catalysts to prepare the highly porous graphitic activated carbon (HPGAC), we propose the hydrothermal pretreatment-assisted chemical activation method to synthesize HPGAC as electrode materials using a small amount of Na-based catalysts (20 wt %). Hydrolysis accompanied by the strong depolymerization and reorganization of the coal framework is beneficial to the removal of different kinds of oxygen-containing structures (including cross-linking bonds, functional groups, and heterocycles) from lignite; thus, the deoxidization effect of hydrothermal carbonization (HTC) on hydrochar gradually strengthens with the increase in pretreatment temperature from 180 to 300 °C, resulting in the formation of a lot of disordered nanostructures and a smooth and compact surface. In the subsequent chemical activation stage, the microstructure of hydrochar is beneficial to the formation of a lot of graphene-like sheets and developed micropores even under a small amount of Na-based catalysts (20 wt %). The as-obtained C-HTC-300 with a highly ordered microstructure and a high specific surface area (SBET) of 1945.33 m2/g has an excellent electrochemical performance. Compared with a large consumption of catalyst for synthesizing HPGAC in traditional chemical activation, the hydrothermal pretreatment-assisted method meets the environmental protection and low-cost preparation requirements.

Highly microporous Parinari Curatellifolia carbon nanomaterials for supercapacitors

High surface area nanostructured electrodes are essential for understanding charge storage mechanisms in high capacitance supercapacitors. Additionally, a growing number of studies provide credible evidence that the highest capacitance in carbon nanomaterials is attainable only when the pore size is in micropore range. In this study therefore, micropore-dominatedcarbon materials derived from Parinari curatellifolia (PC) waste seeds are prepared via pyrolysis and subsequent chemical activation with KOH. SEM, EDAX, TEM, Raman, and XRD studies show that the microstructure and composition of the as-prepared microporous carbon materials are influenced by adjusting the KOH to carbon mass ratio. Sorption studies demonstrate a very high BET surface area of 1898 m2 g−1, type I isotherm, and 99% micropore content in all the samples. The BET surface area, Smicro, Vmicro, and total volume increased with increasing KOH content during activation. The fabricated electrodes exhibit high specific capacitances of 423 F g−1 at 5 mV s−1 and cyclic stability of 98% after 50000 cycles both of which are indicative of our carbon materials huge potential in making high performance supercapacitors. The specific capacitance increased with the micropore content in the samples signifying that the pores enhanced diffusion and hence the charge storage. The PC carbon materials deliver high specific capacitance due to the enhancement of diffusion and charge storage stemming from the synergetic interplay of the aforementioned textural parameters. The PC carbon materials therefore provide good prospects for supercapacitor applications.

Adsorption isotherms and kinetic modeling of methylene blue dye onto a carbonaceous hydrochar adsorbent derived from coffee husk waste

In this study, activated carbon in the form of carbonaceous hydrochar adsorbents with highly functionalized surface-active sites were produced from coffee husk waste via hydrothermal carbonization under low-temperature conditions (180 °C) and subsequent chemical activation. Thereafter, the hydrochars were characterized using diverse analytical techniques, and batch experiments of methylene blue (MB) adsorption were performed under various operating conditions. The results indicated that the activated hydrochar (AH) had a larger specific surface area (862.2 m2 g−1) compared to that of its carbonaceous precursor (33.7 m2 g−1). The maximum MB sorption capacity of the hydrochar activated with potassium hydroxide was extremely high (415.8 mg g−1 at 30 °C). In addition, adsorption isotherms and kinetics were studied using experimental data fitting to further understand and describe the dynamic equilibrium, dynamic kinetics, and mechanism of MB adsorption onto the prepared hydrochars. As compared to the Freundlich isotherm model, the Langmuir isotherm model provided a better fit with the experimental data exhibiting a maximum monolayer adsorption capacity of 418.78 mg g−1. The linear pseudo-second-order kinetic model was found to be suitable for describing the adsorptive kinetics of the hydrochar. The results demonstrated the immense potential of coffee husk waste to produce activated carbon as an alternative green hydrochar that can be applied to dye removal from wastewater as well as improvement of waste management.

Porous Graphitic Carbon Fibers for Fast‐Charging Supercapacitor Applications

Large accessible surface area, facile pore engineering, and high electrical conductivity are highly desirable properties of efficient electrode materials. Herein, porous carbon fibers with a graphitic carbon skeleton and amorphous carbon body are successfully synthesized from directly carbonized polyacrylonitrile (PAN)/FeCl3 electrospun fibers via in situ catalytic graphitization and subsequent chemical activation. Due to the graphitic carbon skeleton, which facilitates fast electron transfer, and porous carbon body, which gives a large specific surface area for charge accumulation and fast ion diffusion, optimal porous graphitic carbon fibers are developed that exhibit a fast‐charging electrochemical performance with a capacitance of 165 F g−1 at high current densities of 300 A g−1 in an alkaline electrolyte. These findings can prove to be beneficial for realizing a supercapacitor with rapid charging and discharging ability at high current densities.

Особенности синтеза нанопористого углеродного материала

Creation of innovative products and technological breakthrough – phrases most often used in relation to objects located in the nanoscale area. Carbon nanomaterials (CNMs) of various morphologies and structures, which include nanotubes, graphene, nanoporous carbon, are one of the most studied materials of the nanotechnology industry at present. This is due primarily to the fact that their physico-mechanical and physico-chemical characteristics have a direct effect on the final product. At the same time, for a number of applications, the best performance is achieved at the highest possible values of specific surface parameters and porosity. Methods and an experimental technology for producing micro- and mesoporous carbon material have been developed. Depending on the feedstock and technological synthesis modes, a nanoporous carbon material is obtained with a predominance of micro- or mesopores, with a BET specific surface area in the range of 2000–4000 m2/g. The technology includes carbonization of the starting materials and subsequent chemical activation. The obtained activated carbon material can be used as sorbents for gaseous media, both in purification systems and as gas batteries for safe storage and transportation systems, as well as for solving a number of environmental problems.

Low thermal conductivity carbon material from electrospinning and subsequent chemical activation

Low thermal conductivity carbon fibers from polyacrylonitrile (PAN) are currently being explored as an alternative for traditional rayon-based carbon fibers with a thermal conductivity of 4 W/m K. Compared to multiple component electrospinning, this research demonstrated another feasible way to make low thermal conductivity carbon fibrous material by electrospinning PAN followed by carbonization and alkali activation. The effects of activation condition on microstructure, pore formation, and thermal conductivity of the resultant carbon nanofibrous material were investigated. The processing-structure-thermal conductivity relationship was revealed and mechanism of thermal conductivity reduction was discussed. The overall thermal conductivity of the prepared carbon nanofibrous material is a result of combined effects from factors of carbon structure and number of pores rather than volume of pores or specific surface area. The activated carbon nanofibrous materials showed thermal conductivity as low as 0.12 W/m K, which is a reduction of ~ 99% when compared to that of solid carbon film and a reduction of ~ 95% when compared to that of carbon nanofibrous material before activation.

Electrospun poly(acrylonitrile-co-itaconic acid) as a porous carbon precursor for high performance supercapacitor: study of the porosity induced by in situ porogen activity of itaconic acid

An acrylonitrile based copolymer, poly(acrylonitrile-co-itaconic acid), P(AN-co-IA) was synthesized with different amounts of itaconic acid (IA) to study in situ porogen activity of IA to produce porous carbon nanofibers (CNFs) without any subsequent physical or chemical activation. The concept developed here avoids unnecessary and complex extra activation steps when fabricating CNFs which ultimately lead to lower char yields and uncontrollable pore sizes. The ability of COOH in P(AN-co-IA) to act as an in situ porogen by releasing CO2 during carbonization was verified by simultaneous thermogravimetric analysis-mass spectrometry compared to polyacrylonitrile (PAN). The specific surface area of PAN CNFs (27 m2 g−1) dramatically increases to 1427 m2 g−1 upon addition of ∼8 wt% IA without any ex situ activation. Furthermore, we confirmed that the porosity could be tuned by changing the IA content. The best electrochemical performance was obtained from the copolymer containing ∼8 wt% of IA, which gives a maximum specific capacitance of ∼93 F g−1 at a scan rate of 10 mV s−1 and energy density of ∼46 Wh kg−1 at 1 A g−1 without any subsequent physical or chemical activation.

Influence of Multiwalled Carbon Nanotubes as Additives in Biomass-Derived Carbons for Supercapacitor Applications.

Glucose-derived carbon/carbon nanotube (CNT) hybrid materials were prepared by hydrothermal carbonization of glucose in the presence of CNTs and subsequent carbonization, physical activation, or chemical activation. The proportion of CNTs added during the hydrothermal polymerization of glucose was varied to ascertain the optimum dose to maximize the performance of the carbon hybrids in supercapacitor applications. Both the thermal treatment applied and the addition of CNTs lead to changes in the textural and chemical properties of the activated carbons. It was observed that samples bearing CNTs exhibit higher number of nucleation centers for glucose oligomers to polymerize, and consequently, the behavior of the hydrothermal carbon toward activation differs according to the activating agent employed. Moreover, the initial chemical speciation dominated by acidic groups shifts to more basic functionalities (quinones and carbonyl groups) with the addition of CNTs. The effect of the different physicochemical properties of the prepared carbons on their electrochemical behavior was evaluated. The addition of 2 wt % of CNTs and subsequent chemical activation leads to electrode materials yielding 206 F g-1 and 78% of capacitance retention up to 0.8 V and 20 A g-1 and high rate cyclability (97% after 5000 cycles). The outstanding performance is ascribed to the high surface area, narrow mesopores, and phenol/carbonyl surface functionalities, which enhance molecular diffusion, the amount of stored energy, and electronic transportation, respectively.

Porous Carrageenan-Derived Carbons for Efficient Ciprofloxacin Removal from Water.

Porous carbon materials derived from biopolymers are attractive sorbents for the removal of emerging pollutants from water, due to their high specific surface area, high porosity, tunable surface chemistry, and reasonable cost. However, carrageenan biopolymers were scarcely investigated as a carbon source to prepare porous carbon materials. Herein, hydrochars (HCs) and porous activated carbons (ACs) derived from natural occurring polysaccharides with variable sulfate content (κ-, ι- and λ-carrageenan) were prepared and investigated in the uptake of ciprofloxacin, which is an antibiotic detected in water sources and that poses serious hazards to public health. The materials were prepared using hydrothermal carbonization and subsequent chemical activation with KOH to increase the available surface area. The activated carbons were markedly microporous, presenting high specific surface area, up to 2800 m2/g. Activated carbons derived from κ- and λ-carrageenan showed high adsorption capacity (422 and 459 mg/g, respectively) for ciprofloxacin and fast adsorption kinetics, reaching the sorption equilibrium in approximately 5 min. These features place the ACs investigated here among the best systems reported in the literature for the removal of ciprofloxacin from water.

Nitrogen and phosphorus co-doped carbon hollow spheres derived from polypyrrole for high-performance supercapacitor electrodes

Nitrogen and phosphorus co-doped carbon hollow spheres (NPCHSs) have been prepared by a carbonization and subsequent chemical activation route using dehydrated polypyrrole hollow spheres as the precursor and KOH as the activating agent. NPCHSs are interconnected into a unique 3D porous network, which endows the as-prepared carbon to exhibit a large specific surface area of 1155 m2 g−1 and a high specific capacitance of 232 F g−1 at a current density of 1 A g−1. The as-obtained NPCHSs present a high-level heteroatom doping with N, O and P contents of 11.4, 6.7 and 3.5 wt%, respectively. The capacitance of NPCHSs has been retained at 89.1% after 5000 charge–discharge cycles at a relatively high current density of 5 A g−1. Such excellent performance suggests that NPCHSs are attractive electrode candidates for electrical double layer capacitors.

Common and Potentially Prebiotic Origin for Precursors of Nucleotide Synthesis and Activation.

We have recently shown that 2-aminoimidazole is a superior nucleotide activating group for nonenzymatic RNA copying. Here we describe a prebiotic synthesis of 2-aminoimidazole that shares a common mechanistic pathway with that of 2-aminooxazole, a previously described key intermediate in prebiotic nucleotide synthesis. In the presence of glycolaldehyde, cyanamide, phosphate and ammonium ion, both 2-aminoimidazole and 2-aminooxazole are produced, with higher concentrations of ammonium ion and acidic pH favoring the former. Given a 1:1 mixture of 2-aminoimidazole and 2-aminooxazole, glyceraldehyde preferentially reacts and cyclizes with the latter, forming a mixture of pentose aminooxazolines, and leaving free 2-aminoimidazole available for nucleotide activation. The common synthetic origin of 2-aminoimidazole and 2-aminooxazole and their distinct reactivities are suggestive of a reaction network that could lead to both the synthesis of RNA monomers and to their subsequent chemical activation.

Glucose-Based Activated Carbon Spheres as Electrode Material for Electrochemical Capacitor

In this work, porous carbon spheres (PCSs) are prepared through hydrothermal treatment of glucose and subsequent chemical activation by KOH. The analysis of pore structure and morphology of the resultant PCSs were characterized by Raman spectra, N-2 sorption technology and electron microscope. The results indicated that the microstructure of activated PCSs can be tuned by varying activation intensity. The PCSs activated at alkali carbon ratio of 4 possess remarkable porosity, extremely large surface area and large pore volume. The well-defined porous structure and high surface area benefited the PCSs to exhibit an excellent charge storage capacity with a specific capacitance of 280 F g(-1) in 6 mol L-1 KOH at a current density of 0.5 A g(-1) and long-term cycling stability over 1000 cycles. The well-developed porous nanostructure together with the excellent electrochemical performances make this study provide new opportunity for hydrothermal carbonization of biomass as electrode materials for energy storage.

Low-cost counter electrodes based on nitrogen-doped porous carbon nanorods for dye-sensitized solar cells

Nitrogen-doped porous carbon nanorods (N-PCNRs) with high accessible surface area are prepared by carbonization of polyaniline (PANI) nanorods and subsequent chemical activation, and explored as the counter electrode in dye-sensitized solar cells (DSCs). SEM and TEM images demonstrate that the nanorod morphology of PANI is preserved after pre-carbonization and chemical activation treatment. The unique combination of the porosity with high accessible surface area, nitrogen doping, and nanorod structure endows the N-PCNR electrode with an excellent electrocatalytic activity for the I3- reduction, which is illuminated by the electrochemical measurements. Under simulated AM 1.5 illumination (100mWcm−2), the DSC based on N-PCNR counter electrode achieves a conversion efficiency of 7.01%, which is nearly close to that of the cell based on Pt counter electrode (7.25%).

Li-ion vs. Na-ion capacitors: A performance evaluation with coconut shell derived mesoporous carbon and natural plant based hard carbon

Coconut shell derived mesoporous carbon (CS-AC) is explored as prospective supercapacitor component in Li-ion and Na-ion capacitors (LIC and NIC) along with pre-lithiated/sodiated natural plant derived hard carbon (HC) as battery element. Though, there is no obvious variation from the capacitive properties of CS-AC, but an obvious difference is evident for battery component in single electrode configuration. Based on such performance, the mass loading has been adjusted during the fabrication of LIC and NIC. Prior to this, HC is pre-lithiated/sodiated for LIC/NIC assembly. The CS-AC and pre-treated HC based materials registered the maximum energy density of ∼121 and ∼82Whkg−1 for LIC and NIC assemblies, respectively. An excellent long-term cycleability of ∼83% retention is noted for LIC after 8000 cycles, whereas NIC showed inferior performance (∼60%) under similar testing conditions. Multilayer surface film is the main reason for such performance which has been clearly revealed from the impedance measurements. First, the CS-AC is prepared by hydrothermal carbonization and subsequent chemical activation with ZnCl2 to yield high specific surface area and pore volume of 1795m2g−1 and 2.2cm3g−1, respectively, in which 71% originated from mesoporous region.